Discriminative alkali halide screen



Feb. 25, 1947. G. R. FoNDA l DISCRIMINATIVE ALKALI HALIDE SCREEN Filed April s, 194s Gor'ton R. Fonda,

, His Attorney.

Patented Feb. 25, 1947 DISCRIMINATIVE ALKALI-.HL'ID'SVCREEN Gorton R.jFonda`,' Schenectady, N. Y.; fassignor to'jGeneral` Electric Companyyalco'rporation of New York 'f Application April 8, 1943, Serial No. 482,276

48 Claims.' (Gli Z50-'164) .L The present invention.. relates .tol cathodev ray l'. taining Vscreens vor lms ofcalkali. halide which are Ysensitiveto vcathode ray `(electron) bombard- Vment.. As the image ortrace made by a. cathf. .ode ray beam on alkalihalide consists of a coloration rather than of anemission of light, as in the case of a fluorescent screen, it is lcustomary toy Irefer to l cathodeA ray tubes containing alkali `halide screens as 1dark tracefftubes.

:the traces to fadeoutfafter .excitation has-ceased,

iis also unlike for';differenthalides.

In Aaccordance with' mypresent 'inventionthese properties have'been-,utilized incathoderay tube ;,halidescreenswhereinthe contrastingr colors as f `Well `as theform 7ofthe.v cathode ray ltraces give valuable information.

' For examplepin one class of `range-finding and direction-linding s equipments electromagnetic .waves are radiatedv and if these-radiations are 'reflected by an object a corresponding kimage o1' vtrace is' formed on the screen of avcathode ray tube forming part of.` such equipment. f In order fto properlyinterpret=suchrvisible imshouldpersist long enough to be noted by an observer, but it is also desirable `that laai-,race produced bythe reflection ofraldiationsdfrom a moving object should contrast .with a trace produced by=reflections from astationaryobject. It ..-..acceleration oftheelectrons yisprovided by a is also desirable'wthat traces produced by'moving devices of the skiatron type, that is,.devices coning vof'fn/1y"'invention 4may be "had -from'- the following description taken 'in -connection with' the accompanyingA drawing.

'1 Fig."1`of the drawingis a conventionalized 'side view of'a' cathode ray tube as illustrative of a .devicefernbodying my invention; and Figs.`2"and 3 areenlarged sectional views conventionally illus- A .trating screens embodying my invention.

. g' Referringparticularly to Fig.- 1, 4thereis shown As a-matter of fact, such halide traces have f .f =distinguishable,fcolors.. vForexample, a cathode '-rayf trace `formed on'potassium chloride is maf genta in-.color,-whereas the. trace formed on rub-idium chloride. is. green. The-so-calledf decay rvperiodythat inthe-length of'time required for schematically a""'cathode ray tube comprising a .glass envelope Whichhas a relatively slender stem .'portion I 0 Tand anLenjlarged bulbous 'portion Il. .The latter" portion is provided with `a'kvvindow l2 through which 'an',observer may'view a luminescent screen which is applied to` theinn'er surface ofthevvindow as indicated at |31 VThe na- 1 L ture 'or the screenfwill be explained in detail at a. later point.

Atthetend of .the 'envelope remote fromvthe .screen l3vthere is 'provided an arrangement for .o generating -.a rcathode raybeam (i. e., a concen- .tratedstream ofy electronsl. l,The means employed for.` this purposer may comprise .any conventional type of electron gun. In. the present instance the. electron` source is illustrated diagrammati- ..cally as comprising anelectrically heatedcathode i6 :which is, enclosed within aV control. or

focusing 'cylinder l1.. .Ordinarily the 'cathode elec- -tron emissionV is enhanced by, a coating of oxides ages or traces it is'desirablenot onlytth'at. they tured .electrode JVor .grid l8which is adapted to be objects should indicate on the screen tlrezdrection of motion of suchobjects.

In cathode ray .tubes embodying my` invention traces produced by; moving objects havec-axcolor diiering from traces produced by stationary obt jects; also" traces-@produced by: moving ,objects fhavea different color as4 Wellfa'sdifferent `inten- :Isity at ornear" the origi'n ofy thetraces than at maintained at a positive .potential With reference totheacylinderand.Whiclrhas the function of` initially 7accelerating the electrons developed bye the.- cathode ,ltowardthe screen I3... Final -A- .terminalfconnection 20 fonthis conductive layer is providedior a: lead-in .conductor 2l.

l* f-Connection of the parts of-A the-.electron .gun and thepoint' where the latestposition ofithe movrwing; object isiindicated.; .'These'@color-'contrasts are vproduced byrther `combination in the screen of a cathode ray tube of alkali halides responding Withdiferent colors tol excitation by cathode :Jrays aslwell as-.having different` rates of decay.

the anode to.- afrsourceof .energy 2.2 bythe conv-.ductorsi 23 2li-.land 25 hasbeen conventionally indicated.

f-Such-apparatus forpresent purposes 4may be :assumed .tofcomprisei the elements of a .rangeandf direction-finding'.equipment, although my ffinvention.i s:applicable to other fields, 'as for exfix-Novel'- features yof-invention, which is-.not ren v.amp1efthe .television field.A '.Depending `upon the 4,nature-.ofthe potentials impressed upon the'equipment with' .which-.the cathodel ray tube is used,

thercathode;raywbeammay fbe.- caused Jto develop Varying traces upon the screen I3, which traces may be interpreted by an informed observer in terms of the factors desired to be ascertained by the use of the equipment.

Satisfactory screens embodying the present invention will be illustrated by the following illustrative examples. v

A lm of potassium chloride or lithium iodide first is deposited by Volatilization from a holder 21 on the surface of a non-conductive, transpar-A andere ent support, such as the glasswindow I2, of the A cathode ray tube. This layermay comprise approximately about 1 to 3 milligrams per square centimeter, which expresses approximately the customary thickness of single layer screens such as heretofore used in cathode ray tubes.v On foundation layer 28, "Fig. 2, 'a secondV f tion `thereof by at least part of the electron beam.

The holders 21 and 30 in which pellets of the f desired halideare placed during assembly of the tube parts are heated by locally .applied higlrfrequency.

The color of a trace or image produced by elec- Vtrons in the foundation film is dark in color. The

potassium chloride coloration is magenta' and the alternatively is brownish-black. The persistence or ratesV of decay of either one of these halides .l is long,'the lithium iodide especially having a Very long persistence.

y Both the color and the persistence of traces formed on the second or top layer are contrasting with the lower layer. Both species of top layers respondto electron impact by forming greenish.- colored traces, the potassium bromide trace being bluish-green. Both toplayer halides are characterized byrapid'decay; that is, short persistence l of traces formed thereon. Hence, such a compound iilmexhibits initially upon Vreceiving the impact of electrons a greenish or greenish-blue trace which quickly changes as the colorformed on rthetop layerfades to a vanishing point leav traces, the most recent of which is greenish in 4 chlorides of other metals may be used, such as samarium, thallium, manganese, sodium, cadmium, lead, chromium, nickel, platinum, caesium, calcium, aluminum, iron, thorium, lithium, rubidium, copper, zinc, zirconium or tin. Ordinarily the period of decay becomes progressively shorter (within limits) with increase of modifier. narily the amount of modifier which is used should be within the limits of a few tenths of one per cent vp to about 5 per cent. The mixture of alkali halide and modifier is subjected to fusion the temperature being regulated not to rise much above the .melting point of the mixture. The fusion temperature should be maintained until the meltedfmass has become clear and transparent and free from vthe agitation which occurs when a fusion heat is first applied. The modified mixture after fusion is ground and compressed into a pellet for insertion inthe holder.

When the lithiumiodide first is vaporized, the resulting film tends to be transparent. It is more satisfactory when whitened by a few minutes exposure tewater vapor at a pressure of about 4.5 to 7.0 millimeters of mercury corresponding to the vapor pressure of vwater at a temperature within the range of about 0 to 6 C., followed by a bake-out before the top film is deposited coloration of lithium iodide which may be used thereon.

A compound nlm. 3|, Fig. 3, of good color contrast can'also'be made by vaporizing simultaneously the 'two halides, such as potassium chloride and potassium bromide, providing it be done by separate operations. In this case, the relative amounts of each one are so adjusted that the ing a dark-colored trace of longer persistence jcharacteristic of the foundation layer.' Consequently a'moving object is denoted by a series-of 'color contrast desired is obtained. Deposition from a suspension in a liquid of thetwo pulverized halides suspended together is an alternative method of producing the lm. However, it is not satisfactory to vaporize a mixture of the two halides.

another.

What I claim as new and desire to' secure by Letters Patent of .the United States is:

l. A cathode ray screen comprising the combination of alkali halides which respond when bombarded with electrons by forming traces of unlike coloration and unlike, persistence.

2. A cathode ray screen comprising the combination of a plurality ofk superimposed layers color and the older ones of which become progressively browner to an extent depending upon their age. These traces of changing color facilitate observations on the change in position of the moving object. Furthermore, they serve to distinguish it from a stationary object because every pulseV of the cathode ray'beam which responds to radiation reflected from such a stationary object will impinge upon the same spot on the screen'so v`noticeable is any alteration in colortoward magenta. By contrast with such a trace, a moving `of alkali halides, said layers responding when bombarded withicathode raysby forming traces of unlike coloration and unlike persistence.

3. A cathode ray screen comprising a layer of potassium chloride and a Vlayer of potassium bromide directly superimposed on said chloride layer.

4. A cathode rayI screen comprising a layer of potassium chloride and a layer of rubidium chloride directly superimposed on said chloride object is represented by a successionl of traces whose color fades into magenta or brown.

The rate of decay of the cathode ray traceof the top layer maybe further decreased by associating the short persistence halide, as for example rubidium chloride or potassium bromide, with a -1 minor amount, ordinarilyless than l() per cent, of

ride of barium,- although' for some purposes the layer.

5. A cathode ray device Ycomprising a glass envelope provided with a window, a coating of luminescent material on said window comprising a plurality of alkali halides which respectively respond to electron excitation by having formed 'therein traces of contrasting color and of unlike persistence.

6. A cathode ray device comprising the combination of a screen which is made up of alkali halides respondingfto electron bombardment byV formingtraces of unlike coloration and unlike persistence, means for subjecting said screen to av 'cathode raybeam and means for moving said Ordi- In this case the color contrast is either poor or absent, Adue to-some interaction between 'the two halides when heated in contact with one 5 beam over said screen to form a linear trace permitting visual observation of color contrasts between different portions of the linear extent of said trace.

7. A cathode ray device comprising the combination of a foundation of glass, a' layer oi alkali halide therein which responds to cathode ray excitation by having formed therein a dark coloration and superimposed thereon a layer of potassium bromide of lesser thickness which responds to cathode ray excitation by having formed therein a contrasting coloration, and means for subjecting said layers simultaneously to a cathode ray beam.

8. A cathode ray screen comprising the combination of a foundation of glass, Ya layer of potassium chloride thereon which responds to cathode ray excitation by the formation of a magenta coloration and a superimposed layer of lesser thickness of a, halide chosen from the group consisting of rubidium chloride and potassium.'

REFERENCES CITED The following referencesare of record in the file of this patent:

UNITED STATES PATENTS 15 Number Name Date 2,330,172 lRosenthal Sept. 21, 1943 2,330,171 Rosenthal Sept. 21, 1943 2,303,563 Law Dec.r 1, 1942 

